Silver-containing microbicides have been incorporated into wound care devices and are rapidly gaining acceptance in the medical industry as a safe, effective means of controlling microbial growth. It has long been recognized that silver plays an important role in promoting wound healing and in preventing infection of the wound. For example, U.S. Pat. No. 3,930,000 discloses the use of a silver zinc allantoinate cream for killing bacteria and fungi associated with burn wounds, and Japanese Abstract 09078430A discloses the incorporation of zirconium phosphate carrying silver into a thermoplastic olefin-based polymer melt for the extrusion of a synthetic antimicrobial fiber. Thus, it is known that placing surface available silver in contact with a wound allows the silver to enter the wound and become ingested by undesirable bacteria and fungi that grow and prosper in the warm, moist environment of the wound site. Once ingestion occurs, the silver kills the bacteria and fungi, which aids in preventing infection of the wound and promotes the healing process.
In addition to containing silver, it is important that wound care devices are capable of moisture management during the various phases of wound healing. For example, immediately after an injury occurs, it is important that the wound care device readily absorbs exudate from the wound site to promote the healing process and help prevent infection. Excess liquid from the wound site, especially if the liquid is allowed to pool, will generally foster a warm, moist environment ideal for microbial growth. During the next phase of granulation, when new cells are generated, it is desirable that the wound care device provides a balanced moist environment. More specifically, to prevent the wound care device from undesirably adhering to the wound site, it is advantageous to design the device so that it absorbs excess exudate, but does not dry out the wound completely thereby causing the device to stick to the new layer of cells that have formed. The final stage of healing typically involves the formation of scar tissue. During this phase, it is important that the wound care device allows the wound to maintain some moisture. Thus, a wound care device having a high degree of breathability is desirable for balancing the exudate absorption capabilities of the device during the various phases of healing.
With the potential for microbial growth at the wound site, another desirable feature of a wound care device is that it absorbs odors emitted by the wound. Especially in chronic, slow-healing wounds, when the application of the wound care device is required for an extended period of time, the lack of oxygen to the wound site may lead to additional bacterial and/or fungal growth. This growth, quite often, leads to infection of the wound and the creation of undesirable odors. Also, in many instances, it is desirable to limit the frequency of changing the wound care device, for instance, in order to not disturb the new cell growth during the healing process. As a result of less frequent changing, the wound care device may develop unwanted odor from association with the wound. Accordingly, the inclusion of an odor receiving agent or layer within or on the wound care device is advantageous.
Furthermore, it is readily known that silver-ion antimicrobial agents, such as ion-exchange compounds like zirconium phosphates, glasses, and/or zeolites, are generally susceptible to discoloration and, due to the solid nature thereof, have a tendency to discolor the substrate in which they are incorporated. More specifically, excess silver ions can combine with available anions to form colored, precipitated salts. Many of these silver salts can darken upon exposure to light as a result of the photo reduction of silver ion to silver metal. This is especially problematic in the medical industry, and specifically in wound care devices, where examination of the wound site as well as the bandage or dressing covering the wound, is an important indicator of the effectiveness of the treatment administered for a particular wound. As such, evidence of discoloration on the wound care device may indicate infection at a wound site. Alternatively, it may be completely unrelated to the status of the wound site and may, instead, be present as a by-product of the degradation of silver ions contained within or on the wound care device itself. Thus, it is important to those in the medical industry that the wound care device itself does not become discolored merely because silver ions are undergoing reduction, which can lead to confusion as to the effectiveness of the treatment being administered to the wound. Accordingly, a stable silver-containing antimicrobial finish on a wound care device is most desirable.
There have been various attempts by others to create wound care devices to address all of the above-identified concerns. In many wound care devices, the microbicide is present throughout the entire cross section of the device. For example, such microbicides have been adapted for incorporation within melt-spun synthetic fibers, as taught within Japanese Abstract 09078430A, in order to provide certain fabrics that selectively and inherently exhibit antimicrobial characteristics. However, such melt-spun fibers are expensive to produce due to the large amount of silver-based compound required to provide sufficient antimicrobial activity, especially in light of the migratory characteristics of the compound from within the fiber itself to its surface. As such, when these silver-containing fibers are combined to form a wound care device, the silver located on the interior of the fiber may never reach the wound site during the useful life of the device to provide any advantage to the healing process. Thus, this provides an inefficient and expensive use of silver in wound care devices, and it is even likely that the amount of silver present on the surface of the fibers is an inadequate amount for promoting the healing process.
Yet another product available on the market is a silver-containing, open-cell foam produced by adding silver to the polymer matrix prior to formation of the foam. The resulting product has silver throughout the entire structure. Generally speaking, the silver in the center of the foam product will never come in contact with the wound site to provide beneficial antimicrobial properties to the wound. Even if the silver Is capable of migrating to the surface of the foam, the frequency with which wound care devices are changed would most likely prevent the silver from achieving any antimicrobial effect on the wound site. Accordingly, much of the silver is used simply to prevent growth of microbes in the bandage itself and is not useful in the treatment of the wound.
Others have attempted to provide composite, multi-layered wound care devices which would achieve all of the desired characteristics described herein. One example includes a multi-layer wound care device comprised of 3 layers—a layer of polyethylene film, a middle layer of rayon/polyester blend nonwoven fabric, and a second layer of film. Nanocrystalline silver particles are deposited onto one or more of the film layers to provide an antimicrobial wound care device. However, this technology generally fails to impart desirable controlled release of silver from the device and the device itself exhibits an undesirable discoloration. Typically, this product will initially release, or dump, large amounts of silver from the wound care device, often in the form of silver flakes which enter the wound bed and lead to irritation of the wound.
Another product available to consumers is a highly porous, silver impregnated charcoal cloth sandwiched between two nylon nonwoven layers containing 220 mg of silver. This product generally provides very low release of silver and the device itself exhibits an undesirable discoloration.
Other attempts have been made to apply such specific microbicides on the surfaces of fabrics and yarns with little success in terms of controlled release of the microbicide to the wound, prevention of discoloration of the wound care device, and adequate exudate absorption capabilities. To make this device, silver via a solution of silver nitrate is reduced and deposited on sensitized polymeric fibers (typically nylon) via a process referred to as electroless deposition. The silver laden polyamide is attached to a subsequent fiber layer. Because of the nature of this technology, it is difficult to control the amount of silver deposited on the fiber and furthermore, the amount of silver deposited is limited by the surface area of the fiber. Additionally, this product faces challenges with regard to discoloration of the substrate as well. Thus, a topical treatment with silver-based antimicrobial agents has not been successfully developed and applied to a substrate having the combination of characteristics described herein, as desired for an effective wound care device.
A topical treatment for textile substrates, such as a fabric, is desirable because it permits treatment of a fabric's individual fibers before or after weaving, knitting, and the like, in order to provide greater versatility to the target yarn without altering its physical characteristics. It is also advantageous for application to foam materials because antimicrobial agents are not incorporated into the material in areas that will never come into contact with the wound. Such a coating, however, should prove to be successful at releasing a controlled amount of silver to the wound while preventing discoloration of the wound care device to be considered functionally acceptable. Furthermore, it is desirable for such a metallized treatment to be electrically non-conductive on target fabric, fiber, yarn, film and/or foam surfaces. With the presence of metals and metal ions, it has been difficult in the past to obtain such a functional, electrically non-conductive coating for use in wound care devices.
Successful attempts at topically applying a silver-based antimicrobial finish to textile substrates are described in commonly assigned U.S. Pat. No. 6,584,668 and in commonly assigned U.S. patent application Ser. Nos. 09/586,381; 09/586,081; 09/589,179; 09/585,762; 10/307,027, and 10/306,968. All of these patents and patent applications are herein incorporated by reference. The details of many of these processes will be discussed in detail below.
The present invention addresses and overcomes the problems described above. Historically, a microbicide has been incorporated into a melt or polymer matrix prior to the formation of a fiber, foam, or other textile substrate to create an antimicrobial layer useful for wound care devices. The current invention discloses a method for achieving a wound care device having a silver-based antimicrobial finish, which is topically applied to a target substrate. The resultant wound care device provides controlled release of silver to the wound site without discoloring the device and further provides exudate absorption capabilities. The wound care device optionally includes an odor absorbing agent or layer for eliminating or reducing undesirable odors emitted from the wound site. Additional layers may also be included in the composite structure to assist in boosting absorption capacity, such as, for example, one or more layers of foam, alginate, carboxymethyl cellulose, and the like. These additional layers may or may not contain an antimicrobial agent. For these reasons and others that will be described herein, the present wound care device represents a useful advance over the prior art.